Berlinite has the potential for replacing .alpha.-quartz in bulk and surface acoustic wave applications because it combines low loss with higher piezoelectric coupling factors; about two and one-half and four times for bulk and surface waves, respectively. It also has a locus of zero temperature coefficient cuts. Because of these properties, Berlinite can be used in crystal oscillators and filters, and in devices involving long delay lines for electronic warfare, surveillance and target acquisition, pulse compression, and signal correlation.
Heretofore, Berlinite has been prepared by addition of aluminum orthophosphate to a seeded orthophosphoric acid contained in a platinum or silver ampule. The ampule is sealed and placed in a Morey-type of Tem-Pres type high pressure autoclave. The temperature of this hydrothermal growth setup is raised slowly over a period of several weeks. The autoclave is then cooled and the ampule is removed from the autoclave, opened and the crystal is removed from the orthophosphoric acid. The crystals of Berlinite grown by this technique generally have imperfections such as veiling, channeling, cracking, and surface damage.